The following commit has been merged into the x86/core branch of tip:
Commit-ID: 5a9c361a416fc3a3301e859ff09587cc1b933eb8
Gitweb: https://git.kernel.org/tip/5a9c361a416fc3a3301e859ff09587cc1b933eb8
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Mon, 11 Jul 2022 11:49:50 +02:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 17 Oct 2022 16:41:09 +02:00
objtool: Allow STT_NOTYPE -> STT_FUNC+0 sibling-calls
Teach objtool about STT_NOTYPE -> STT_FUNC+0 sibling calls. Doing do
allows slightly simpler .S files.
There is a slight complication in that we specifically do not want to
allow sibling calls from symbol holes (previously covered by STT_WEAK
symbols) -- such things exist where a weak function has a .cold
subfunction for example.
Additionally, STT_NOTYPE tail-calls are allowed to happen with a
modified stack frame, they don't need to obey the normal rules after
all.
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
---
tools/objtool/check.c | 74 ++++++++++++++++++++++++++----------------
1 file changed, 47 insertions(+), 27 deletions(-)
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index e532efb..7936312 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -129,16 +129,13 @@ static bool is_jump_table_jump(struct instruction *insn)
static bool is_sibling_call(struct instruction *insn)
{
/*
- * Assume only ELF functions can make sibling calls. This ensures
- * sibling call detection consistency between vmlinux.o and individual
- * objects.
+ * Assume only STT_FUNC calls have jump-tables.
*/
- if (!insn_func(insn))
- return false;
-
- /* An indirect jump is either a sibling call or a jump to a table. */
- if (insn->type == INSN_JUMP_DYNAMIC)
- return !is_jump_table_jump(insn);
+ if (insn_func(insn)) {
+ /* An indirect jump is either a sibling call or a jump to a table. */
+ if (insn->type == INSN_JUMP_DYNAMIC)
+ return !is_jump_table_jump(insn);
+ }
/* add_jump_destinations() sets insn->call_dest for sibling calls. */
return (is_static_jump(insn) && insn->call_dest);
@@ -1400,21 +1397,18 @@ static void add_return_call(struct objtool_file *file, struct instruction *insn,
list_add_tail(&insn->call_node, &file->return_thunk_list);
}
-static bool same_function(struct instruction *insn1, struct instruction *insn2)
-{
- return insn_func(insn1)->pfunc == insn_func(insn2)->pfunc;
-}
-
-static bool is_first_func_insn(struct objtool_file *file, struct instruction *insn)
+static bool is_first_func_insn(struct objtool_file *file,
+ struct instruction *insn, struct symbol *sym)
{
- if (insn->offset == insn_func(insn)->offset)
+ if (insn->offset == sym->offset)
return true;
+ /* Allow direct CALL/JMP past ENDBR */
if (opts.ibt) {
struct instruction *prev = prev_insn_same_sym(file, insn);
if (prev && prev->type == INSN_ENDBR &&
- insn->offset == insn_func(insn)->offset + prev->len)
+ insn->offset == sym->offset + prev->len)
return true;
}
@@ -1422,6 +1416,32 @@ static bool is_first_func_insn(struct objtool_file *file, struct instruction *in
}
/*
+ * A sibling call is a tail-call to another symbol -- to differentiate from a
+ * recursive tail-call which is to the same symbol.
+ */
+static bool jump_is_sibling_call(struct objtool_file *file,
+ struct instruction *from, struct instruction *to)
+{
+ struct symbol *fs = from->sym;
+ struct symbol *ts = to->sym;
+
+ /* Not a sibling call if from/to a symbol hole */
+ if (!fs || !ts)
+ return false;
+
+ /* Not a sibling call if not targeting the start of a symbol. */
+ if (!is_first_func_insn(file, to, ts))
+ return false;
+
+ /* Disallow sibling calls into STT_NOTYPE */
+ if (ts->type == STT_NOTYPE)
+ return false;
+
+ /* Must not be self to be a sibling */
+ return fs->pfunc != ts->pfunc;
+}
+
+/*
* Find the destination instructions for all jumps.
*/
static int add_jump_destinations(struct objtool_file *file)
@@ -1519,18 +1539,18 @@ static int add_jump_destinations(struct objtool_file *file)
strstr(insn_func(jump_dest)->name, ".cold")) {
insn_func(insn)->cfunc = insn_func(jump_dest);
insn_func(jump_dest)->pfunc = insn_func(insn);
-
- } else if (!same_function(insn, jump_dest) &&
- is_first_func_insn(file, jump_dest)) {
- /*
- * Internal sibling call without reloc or with
- * STT_SECTION reloc.
- */
- add_call_dest(file, insn, insn_func(jump_dest), true);
- continue;
}
}
+ if (jump_is_sibling_call(file, insn, jump_dest)) {
+ /*
+ * Internal sibling call without reloc or with
+ * STT_SECTION reloc.
+ */
+ add_call_dest(file, insn, insn_func(jump_dest), true);
+ continue;
+ }
+
insn->jump_dest = jump_dest;
}
@@ -3309,7 +3329,7 @@ static int validate_sibling_call(struct objtool_file *file,
struct instruction *insn,
struct insn_state *state)
{
- if (has_modified_stack_frame(insn, state)) {
+ if (insn_func(insn) && has_modified_stack_frame(insn, state)) {
WARN_FUNC("sibling call from callable instruction with modified stack frame",
insn->sec, insn->offset);
return 1;
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